Increasing awareness of the interconnection between wastewater and potable water systems has created new opportunity to purify used water as a significant source of drinking water supply. Ozonation followed by biofiltration using granular activated carbon (GAC) as a medium for biofilm formation creates an O3-biological activated carbon (BAC) treatment train that provides collective technical advantages of adsorption, oxidation and biodegradation of pollutants remained in secondary effluent in an economical way. In order to exam the technical potential and robustness of this treatment train for potable water reuse, eight pilot-scale O3-BAC trains were operated in parallel to purify the secondary effluent that has been further processed by multi-media filtration and deep bed GAC filtration at Upper Occoquan Service Authority. In an attempt to further improve the process cost-effectiveness and sustainability, this study also compared O3-BAC performance with spent or regenerated GAC as biofiltration media. Experimental results showed that, other than the initial pollutant adsorption capacity shown during system startup, the regenerated GAC demonstrated almost two-fold more pollutant removal efficiency than that of the spent GAC at steady-state. This may be a result of more surface area for additional bacterial retention or enhanced driving forces that increase substrate diffusion through the biofilms. Moreover, the organic pollutant removal by biofilms growing on both spent and regenerated GAC were shown to significantly increase with the ozone dose but decrease with the empty bed contact time. It was confirmed in this study that ozonation/chlorination byproduct formation can be reduced significantly through optimizing the ozone dose and empty bed contact time. The organic matter signature plots revealed from fluorescence excitation emission matrix (FEEM) results further showed that O3/BAC can produce water with a FEEM signature approaching ultrapure water, which reinforces confidence in applying O3/BAC for potable reuse.

Pilot-scale investigation of ozone-enhanced biofiltration using spent and regenerated granular activated carbon media for potable reuse

254th National Meeting (2017)

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